Scott Alexander, as usual, addresses things interestingly and sanely. And he disagrees with you. Worth reading:

https://slatestarcodex.com/2017/08/07/contra-grant-on...

By graduating elementary school?

I think that much more likely plan-Bs (certainly career-wise) include studying informatics, information-system, industrial engineering, or simply computer-science in a less prestigious college. I doubt there are many who study math for any other reason than the love of it (at least not for their first degree).

Besides, girls do as-good (if not better) than boys in school, aren't they? So how can grades be an explanatory factor to begin with?

What's the big difference between 1700-hours long training, to (at least) 1400-hours long training? It's a similar entry barrier.

ASAIK, basic training is several months there after they get their first assignments. You don't imply that it takes some 3 years training before IDF starts to get its money worth?

The most basic program (least prestigious, minimal prerequisites) indeed extends over just 6 months. But those are dense and intensive 6 months, that in terms of academic-hours worth over 80% of 3 years of college (~1400 hours vs. ~1700 hours). Soldiers in this program are required to serve 6 years, exactly because this training is hardly enough, and in practice it takes another 1-2 years of OJT and further courses before they become reasonably qualified.

First part of your response is qed.

I thought we were talking about entry-barriers and qualification requirements.

Precisely. The current discussion opened by comparing veterinary to programming. The former requires 7 years plus to qualify, the latter, as you've aptly pointed out, can be accomplished with several months of training.